Continuous method of steel making

ABSTRACT

Steel is made continuously by mechanically agitating molten pig iron and slag proximate their interface and simultaneously passing oxygen onto that interface whereupon the pig iron is desulphurized and dephosphorized. The pig iron product is then decarbonized by treatment with oxygen.

United States Patent [191 Ando et al." 1*Aug. 28, 1973 [54] CONTINUOUSMETHOD OF STEEL 2,767,077 10/1956 Perrin 75/52 MAKING 2,856,280 10/1958von Bogdandy 75/60 2,962,277 1 1/1960 Morrill 75/60 X -Inventors: yAndo; Tsutomu Fukushima. 2,975,047 3/l96l Leroy et al. 75/60 x both ofKawasaki-shi, Japan 3,013,789 l2/l96l Sayre et a1 266/36 3,171,8773/1965 Thrin 75/46 X 73 Ass1gnee: Nippon Kokan Kabushlki Kaisha, I3.172.756 3,1965 aengson 75,60 x 1 Kanagawar Japan 3,303,018 2/l967 Goss75/60 X a: 3,331,681 7/1967 Mobley 75/60 I Nome gigggggg: 3,567,2043/1971 Ando et al..... 266/34 p q y 3,592,629 7/1971 Ando et al. 75/58has been d1scla1med. [22] Filed: y .2, 1969 FOREIGN PATENTS ORAPPLlCATlQNS 373,358 2/1962 Japan 75/46 [21] Appl. No; 821,385 594,9963/1960 Canada 75/60 Prima Examiner-L. Dewa ne Rutled e 30 F A 11 ti P Dm Y 8 1 orelgn pp ca on Horny a Assistant Examiner-M. J, Andrews May 9,1968 Japan 43/30563 Atmmey Flynn and Frishauf 52 US. Cl 75 46 75 52, 7558, 1 75060 57 ABSTRACT [51] Int. Cl. C2lc 7/00, C2lc 7/06 St l s a slyy ni a ly agitating [58] Field of Search 75/46, 52, 60; molten pig ironand slag proximate their interface and 266/34, 35 simultaneously passingoxygen onto that interface whereupon the pig iron is desulphurized anddephos- [56] References Cit d phorized. The pig iron product is thendecarbonized by treatment with oxygen.

8 Claims, 1 Drawing Figure v l CONTINUOUS METHOD, OF STEEL MAKINGRELATED APPLICATIONS:

This application is related to application'Ser. No. 818,283, filed Apr.22, 1969.

FIELD OF INVENTION BACKGROUND OF INVENTION:

With the development of modern metallurgy, there is a tendency ofgradually shifting from conventional batch system steel making (forexample, flat furnace steel, converter steel, or electric furnace steel)to continuous steel making which is more efficient and economical, andvarious methods of continuous steel are now being investigated. However,most of these methods of steel making are those developed from the flatfurnace or converter type, and the basic reaction conditions and therefining conditions are not changed so much as compared with those whichprevailed heretofore. The so-called continuous steel making processinvolves a mere addition of a conventional method of treatment to themolten pig which is continuously moving. Furthermore, several newmethods have recently been published, that is, processes such as spraysteel making and the IRSID tank system, that is the tank system ofInstitut de Recherches do la Siderurgie Francaise.

In the spray steel process, desulphurization, dephosphorization, anddecarburization are effected simultaneuously and momentarily, thus it ismerely a simple refining method for producing low carbon" steel. Also,as the system becomes larger, higher oxygen pressures are required,which introduces considerable problems.

In the IRSID tank system, oxygen is blown through an oxygen lance orthrough porous bricks at the bottom of the furnace, and refining iscarried out by forming an emulsion of slag metal. In this case,temperature regulation is extremely difficult, and the high-temperatureemulsion appears to attack the fireproof material of the furnace, whichis a disadvantage in that the continuous operating period must belimited.

Advantageous points of the continuous method of steel making are asfollows:

1: Low cost of construction (equipment becomes smaller when plants ofequal annual production are compared) I 2: Low operational cost(excellent in thermal efficiency and in available percentage, smallerwear in refractory material, lowering of original unit cost of 0,)

3: Wider allowable operational conditions (substantial proportion ofscrap iron can be used, with less fumes produced. Not only having alarger allowance in extent of variation of materials, but also simplerinoperation with lesser labor force) 4: Improved reliability in quality ofproducts.

(Efficient control and measurement of the chemical reaction).

Although the continuous method of steel making has such advantageousfeatures, there are present disadvantages such as stated before, so thatno satisfactory process has yet been developed. Especially concerningthe reliability in the quality of products as well as the wear of therefractory materials, there are considerable problems left unsolved, andat present, no generally acceptable process has been commercialized.

SUMMARY OF INVENTION In accordance with the present invention, there isprovided a process for manufacturing steel continuously wherein sulphurand phosphorous are removed from molten iron or molten iron alloy priorto effecting substantial decarburization thereof. Slag and molten ironor molten iron alloy are agitated mechanically proximate their interfaceand oxygen is passed simultaneously onto their interface. Thereafter,oxygen is injected into the molten iron or molten iron alloy to effectsubstantial decarburization.

In the process, desulphurization can be accomplished independently bycontacting the molten iron or molten iron alloy with a slag formingagent, in the absence of oxygen preferablyjwith the indicated mechanicalagitation. The treated iron or iron alloy and slag can then be processedas stated above.

BRIEF DESCRIPTION OF THE DRAWING Advantages of the invention will becomeapparent to those skilled in the art from the following descriptionconsidered in conjunction with the drawing wherein:

The FIGURE is a schematic flow diagram illustrating an embodimentwherein desulphurization, dephosphorization and decarburizing are shown.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS As shown in the drawing, pigiron 2 (containing: C=4.3%, Si=0.68%, Mn=0.65%, P=0.l90%, S=0.043%),which is tapped at a rate of 2 tons per minute continuously from blastfurnace 1, is passed through line 20 into desulphurization treating tank3 (capacity [0 tons), which is provided near said blast furnace 1.Calcium carbide (2 kg/min), a slag making agent is passed into tank 3through feeder 4. Desulphurizing of the pig iron is effected whileeccentrically agitating continuously the materials in the area near theslag-metal interface by means of agitating rods 5 made of carbonaceousmaterials and other refractory materials such as refractory clay of highalumina composition (three rods are fitted). Further details of such anagitation operation are provided in copending application Ser. No.818,283, filed on Apr. 22, 1969.

Slag can be removed from tank 3 via slag-removing line 17, and can berecycled (not shown) to tank 3 if desired. I

The pig iron thus treated is passed from tank 3 through outlet line 21to a tank 6 (capacity 10 tons) for dephosphorizing treatment. Slagproducing agent a kg/min. of calcined lime, 30 kg/min. of mill scale, 30kg/min. of soda ash (Na,CO,), l0 kg/min. of fluorite, CaF, or 20 kg/pigton, l0 kg/per pig ton of mill scale, 3 kg/pig ton of fluorite, CaF,) ispassed through feeder 9 and charge line 22 to tank 6, and at the sametime oxygen is injected into tank 6 for a total amount of 30 Nmlmin.through oxygen lances 10 (three lances are equipped) provided on tank 6,while agitating by means of an interface agitating device havingagitating rods 5 made of carbonaceous materials and other refractorymaterials as in the case of said tank 3 so as to remove phosphorus byoxidation. The pressure of the oxygen then injected is from about 2kg/cmto about 3kg/cm In this case slag is removed from slag-removing line 17,and can be recycled (not shown) to tank 6 when necessary.

The treated pig iron is then passed from tank 6 through line 11 to steelmaking furnace 13 (three units) of pure-oxygen, top-blown converter typeprovided on turret-type, rotating table 12, and the decarburizingrefining is effected by conventional processing in which oxygen isinjected through lance M. The slag is also removed from tank 6 throughline 11. In this way, blank steel of medium carbon content containing0.25% of C, 0.006% of S, 0.008% of I, a trace of Si, and a trace of Mn,is obtained. Finally, by introducing a ferro alloy as a deoxidizingagent at the final step of steel making, the desired steel product isobtained. The three units of decarburizing steel making furnacesprovided on said turret-type rotating table 12 are adapted to cooperateeffectively, each operating alternatingly as a decarburizing furnace 13aduring receiving pig iron, a furnace 13b during blowing refining, andfurnace (not shown) during topping and scrapping.

In the above embodiment, the desulphurization and the dephosphorizationare effected using separate treating tanks, 3 and 6, respectively. Whendesulphuriwhich a large quantity of slag is produced, can be efzationand dephosphorization are carried out, it is preferable, as viewed fromsuch stand points as improvement in thermal efficiency, early forming ofslag, and maintenance of fluidity of slag, to utilize slag which isremoved continuously from the blast furnace.

In order to increase the effects of the desulphurization,dephosphorization and decarburization to their maximum, it will besufficient only to increase the number of units of each of the treatingtanks (3, 6, and 13), or to increase the capacity of each of saidtreating tanks. Furthermore, the use of the turret rotating table at thefinal processing, and the provision of a plurality of steel makingfurnaces on the table are essential from view points that the amount ofscrap used can be selected freely, and that the steel making furnace canbe utilized as a ladle. Thus, while one of the steel making furnaces. isunder refining operation, another steel making furnace can be used forpreheating the scraps, or utilizing it as a ladle for molten steel, orusing it as a receiving tank of pig iron which has been subjected to thefirst processing; thus they have a wide range of utility.

The continuous steel making furnace according to the present inventionis characterized by the fact that the desulphurization anddephosphorization process, and that, in said desulfurization anddephosphorization process, the mechanical agitation is effected at theinterface of slag and metal. Thus, in the conventional continuous steelmaking furnace, the principal object thereof is the decarburization, andthe steel obtained is a simple blank steel having a low carbon contentwhich requires one further step to finish it into a desired kind ofsteel. In the continuous steel making furnace according to the presentinvention, low sulphur and low phosphorus steel can be obtained easily,control of each of these components can be effected readily followingthe fected at a relatively low temperature, and although the temperaturerises so much at the final stage of the decarburization, almost no slagis produced in this stage, so that wear loss due to melting ofrefractory material in the desulphurizing and dephosphorizing tank isreduced remarkably. In the furnace according to the present invention,resulphurization and re-phosphorization in the decarburization processcan be prevented because substantially complete removal of slag iseffected in the desulphurization and dephosphorization processing stageor stages.

While the invention has been shown and described in relation to thecontinuous method of steel making, it should be clear to those skilledin the art that the described method of treatment for dephosphorizationand desulphurization is also effective for de-chromiumization andde-manganization.

What is claimed is:

1. A continuous process for manufacturing steel, comprising thesequential steps of a. continuously charging to a refining vessel molteniron or molten iron alloy containing sulphur, phosphorus and carbon,

b. contacting continuously said iron or iron alloy with a slag formingagent in said vessel .while agitating mechanically said iron or ironalloy and said agent at the area proximate the interface thereof,contacting continuously the resulting iron or iron alloy obtained in (b)with a slag forming agent and with oxygen, while agitating mechanicallysaid resulting iron or iron alloy and said agent at the area proximatethe interface thereof, said oxygen being charged onto said interface,and

d. charging continuously the resulting product of (c) to a furnace andinjecting continuously oxygen into said product to substantiallydecarburize said product.

2. The process of claim 1, wherein the molten iron is pig iron.

3. The process of claim 11, wherein the slag forming agent of (b) iscalcium carbide.

4. The process of claim I, wherein the slag forming agent of (c)comprises a mixture of calcined line, mill scale, soda ash and CaF 5.The process of claim 1, wherein the furnace in (c) is a top-blown oxygenconverter furnace.

6. The process of claim 1, wherein the pressure of oxygen in step (c) isfrom about 2 kg/cm to about 3 kg/cm.

7. The process of claim I, wherein said furnace comprises a plurality ofrevolving furnace units.

8. The process of claim 5, wherein said furnace comprises a plurality ofrevolving furnace units.

2. The process of claim 1, wherein the molten iron is pig iron.
 3. Theprocess of claim 1, wherein the slag forming agent of (b) is calciumcarbide.
 4. The process of claim 1, wherein the slag forming agent of(c) comprises a mixture of calcined line, mill scale, soda ash and CaF2.5. The process of claim 1, wherein the furnace in (c) is a top-blownoxygen converter furnace.
 6. The process of claim 1, wherein thepressure of oxygen in step (c) is from about 2 kg/cm2 to about 3 kg/cm2.7. The process of claim 1, wherein said furnace comprises a plurality ofrevolving furnace units.
 8. The process of claim 5, wherein said furnacecomprises a plurality of revolving furnace units.